| OCR Text |
Show Spent Fuel Combustion: For SFG firing, non-luminous flames were observed and stable combustion was possible due to the wide range of flammability limits expected for hydrogen. NOx can be reduced to a level of 1 - 15ppm (~ = 7% equivalent) as compared with 50 - 200ppm for methane flames. This trend is due to the lower flame temperature for SFG. The adiabatic flame temperature is estimated as 1826K for SFG and 2340K for methane, respectively, under the conditions of an excess air ratio of 1.2 and an air preheat level of 673K. Also, the heat extraction rate is approximately 20% lower for SFG flames than that of equivalent methane flames. Spent Air Combustion: Spent air combustion was tested with Type A and Type B burners under the atmospheric pressure condition. Stable combustion was possible, with the simulated spent air at an oxygen concentration level of 9%. This can be expected due to the fact that hydrogen can be burned with diluted air at an oxygen concentration level as low as 6%. As a broader range of the flammability limit can be expected for pressurized flames, the effect of pressure is not considered important. [4] For these specific burners, the increased flow rate for spent air enhanced mixing, thus resulting in a satisfactory flame performance. A potential problem may be that flame detection becomes more difficult as flame transparency increases due to increasing inert gas flow. 2.3 The Effect Of Pressure On Flames Flame Pattern : The effect of pressure on flame patterns can be seen in Figure 3, where on-axis and radial temperature distributions and radial ~ concentration profiles for different pressure levels are indicated. As shown in Figure 3.a, flames for Type D burner are insensitive to a change in pressure level. Although the flame luminosity changes from non-luminous to weak luminous with increasing pressure levels, no substantial change in flame pattern was identified. In contrast to this burner, temperature distributions for Type C burner change with varying pressure levels. As indicated by gas concentration profiles, combustion was delayed for pressurized flames. The increased CO concentration on the axis, especially, indicates poor mixing. Total Heat Extraction: The effect of pressure on the total heat extraction from flame is shown in Figure 4. The extraction rate is a weak function of pressure, as described in the form of Q/Qoapn. In general, n = 0.1 for methane and n = 0.26 for SFG flames. Although flame luminosity for methane firing significantly increases with increasing pressure, the effect is rather 6 |
